1. Field of the Invention
The present invention relates to facilities for cultivating fish.
2. Description of the Prior Art
Conventionally fish reserves for cultivating fish have been formed as follows.
(a) A predetermined space in the water of a bay is enclosed with nets, and the space thus made enclosed is used as a fish reserve for cultivating such fish as yellowtail, sea bream, flatfish and the like.
(b) A box with a certain volume is made of wood or steel sheets, and the box filled up with sea-water is used as a fish reserve for cultivating fish.
(c) A wooden box is partitioned with nets and is used as a fish reserve.
It has conventionally been necessary to arrange fish reserves such as those mentioned above in the water of a bay or by the sea shore. However, due to an insufficient circulation of sea water in bays or in waters by the sea shores, contamination of sea water has often occurred as a result of longterm drifting or accumulation of fish leftovers and droppings on the bottom of the reserve. Sea water contamination is also easily accelerated by an inflow of sewage into the sea from factories located along a nearby coast. Because of this, the mortality rate of cultured fish has been high and the growth of cultured fish has been less than normal. Moreover, the fish which has been cultivated is often contaminated by harmful substances contained in sewage discharged from such factories.